Jitter and noise are commonly known among electrical engineers and similar specialists to cause signal quality problems in high-frequency signals. In general, jitter can be thought of as the “horizontal” displacement of various aspects of pulses in a high-frequency signal or waveform, and noise can be thought of as the “vertical” displacement. Various types of sources can contribute to the overall jitter and noise of a signal such as by electromagnetic interference, cross-talk, data dependent effects, random sources, and so forth. The impact of jitter or noise on a signal can be detrimental to signal quality, particularly in high-frequency systems. As a result, engineers and other designers are mindful of these effects, which can often dictate the design approach for circuit elements, the kind and quality of communication links used in a particular system, the frequency by which signals are transmitted, among other considerations.
Jitter can be decomposed into components to aid in the analysis of the total jitter of a system using a test and measurement instrument such as an oscilloscope. Conventional approaches for decomposing jitter include separating deterministic jitter (DJ) from random jitter (RJ), and then “reassembling” or convolving the jitter components for analysis of the total jitter at a specific bit error rate (BER), sometimes referred to as TJ@BER. During the separation of DJ from the RJ, certain unrecognized periodic and/or aperiodic bounded jitter components may be erroneously included in the RJ. Such mis-qualification is pernicious to any attempts to extrapolate the total jitter amount, since the random component is typically greatly multiplied to calculate TJ@BER. In other words, the exaggerated RJ results in a greatly exaggerated estimation of total jitter of the system.
Relatively recently, the art of jitter analysis has embraced a methodology that plots jitter histograms on a “Q-scale” and uses the asymptotic behavior of the plot to infer the sigma value for the RJ. Known disclosures of this method, for example as specified in the PCI Express Gen 3 standard, apply it to the composite or aggregate jitter or to jitter from which a data-dependent component has been removed. In these applications, any periodic jitter has not been first removed by spectral analysis or other methods. However, the presence of periodic jitter in the distribution can bias the RJ sigma thus inferred, and therefore yield a total jitter calculation of lesser accuracy than would otherwise be obtainable.
Such limitations prevent users of the oscilloscope or other test and measurement instrument from accurately estimating the total jitter of a waveform. Without more precise measurements, it is difficult or impossible to diagnose the source of the jitter, let alone design a system for preventing the jitter from interfering with the quality and integrity of the signal. It would be desirable to more accurately estimate the random jitter, and therefore, the total jitter of a signal so that signal quality can be improved.
Accordingly, a need remains for methods and systems for isolating and analyzing jitter components using spectral analysis and time-domain probability density.